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        <td class="header">&nbsp; Three-Pass DInSAR (InSAR operator)</td>
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<h3>Three-Pass Differential Interferometry</h3>

<p>
    Three-pass DInSAR, stands for three-pass differential interferometry. It is a method to remove the topographic
    induced phase from an interferogram that contains topographic, deformation, and atmospheric components.
</p>

<p>
    This step can be performed only if an unwrapped topography interferogram (topo pair) and a complex deformation
    interferogram (defo pair) are present. Both defo and topo pair has to be referenced to a a common master. This can be
    achieved by processing a stack of interferograms in JLinda. Both defo and topo interferograms have to be corrected
    for the phase, and sampled on the same grid (see Coregistration and Wrap Operator). Also, both defo and topo
    interferograms must have the same multilook factors and the same dimensions (i.e. overlap exactly).
</p>
<p>
    Recommendation is that the perpendicular baseline of the topo-pair should be larger than that of
    the defo-pair. This ratio is recommended in order to prevent that noise is "blown up". Of course, this geometry
    cannot be always controlled, and it rather depends on the available data.
</p>

<p>
    This operation is performed in the stack processing tree. First create a stack of interferograms, that coregistered to the
    same master and processed until subtraction of the reference phase. Then we have to unwrap defo-pair. In order to do so,
    the deformation pair has to be selected, and extracted for the external unwrapping in the Snaphu software. After the unwrap
    is performed externally, the unwrapped results are imported back into the Toolbox. Finally, for DInSAR operators, both
    defo-pair and topo-pair are listed as a source products, and the output of the operator is a differential intereferogram.
</p>
<p>
    To geocode the differential phase values, standard geocoding can be applied.
</p>


<h4>Operator parameters:</h4>&nbsp;&nbsp;

<p>
    This operator performs without any parameters, all the necessary processing information is constructed using
    product metadata. The only input parameter is the control flag for the degree of the orbit interpolator.
</p>
<ol>
    <li>
        <b>Orbit interpolation degree:</b> Defaults to a polynomial of degree (number of state vectors)-1, but smaller
        than degree 5.
    </li>
</ol>

<h4>Source Products:</h4>&nbsp;
<!--&nbsp;-->
<p> Source Products are stack of:</p>

<ol>
    <li>
        <b>Defo-pair:</b> Interferometric product containing bands of so-called defo-pair. See operator description for more details.
    </li>
    <li>
        <b>Topo-pair:</b> Interferometric product containing bands of so-called topo-pair. Topo-pair interferogram has to be unwrapped, and stored as 'real' data band. See operator description for more details.
    </li>

</ol>

<h4>Output bands:</h4>&nbsp;
<!--&nbsp;-->
<p> Output Bands are stack of differential interferograms. The amplitude is the same as that of the original
'deformation' interferogram.  A complex value (0,0) indicates that for that pixel unwrapping was not performed correctly.
</p>

<!--<h4>Implementation notes:</h4>&nbsp;-->
<!--&lt;!&ndash;&nbsp;&ndash;&gt;-->
 <!--<p><i>(More details on algorithmic implementation COMING SOON!)</i></p>-->

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